The present invention relates to positive yarn feed devices and techniques, in particular for feeding yarns to circular knitting machines.
The yarn feeding of half hose knitting machines presents considerable problems, it conventionally not being possible to knit socks which are dimensionally stable. The climax to the process of sock making is normally a tedious pairing operation, which is necessary to ensure that the socks of a pair thereof when sold, washed and worn remain dimensionally matched. Socks knitted in certain yarns and stitch constructions can come off the knitting machine with a size variation with respect to the nominal size of as much as .+-.1 inch.
Changes in stitch density in fabrics coming from any knitting machine or bank of knitting machines result from variables in the knitting process, such as yarn tension and needle friction among others. In the case of half hose production these variables exhibit themselves in the form of size variation due mainly to the cumulative effect of small changes in stitch length.
To overcome these problems the concept of positive yarn control has been introduced, using positive yarn feed devices which are mounted on the creel frame which supports the yarn packages and which are driven mechanically from the knitting machine. The need for the mechanical drive restricts the scope for positioning of the creel frame, complicates the knitting machine and makes it difficult, in some cases impossible, to fit positive feed devices to existing knitting machines. In addition the drive may overload the motor driving the knitting machine, and high loads with associated wear and failure are imposed on the drive shafts and couplings. Furthermore, for garment manufacture and particularly for sock manufacture the yarn feed needs to be programmed throughout the mechanical cycle of the machine during garment production. Such programming is difficult and essentially limited in scope with the mechanically-driven devices.
For the mechanically-driven positive feed of yarn pin wheel and tape drive mechanisms have been developed. Such mechanisms are well known, with the yarn passing around the pin wheel beneath the tape which is continuous and also passes around a so-called quality wheel by which it is driven to provide a positive feed of the yarn gripped between the tape and the pin wheel. The quality wheel is of calibrated and variable diameter, so that the tape speed and hence the yarn feed can be adjusted to draw the yarn from its package and deliver it to the knitting needles at a constant and predetermined rate suited to the knitting procedure.
An advantage of a pin wheel mechanism is that by changing the inlet path of the yarn it can be slipped from under the tape to provide a free running yarn. If, in the case of half hose, the leg and the foot can be knitted under positive yarn feed it is of little significance that the yarn is free running during knitting of the toe, heel, and welt of the sock. The present invention is of particularly valuable application to devices incorporating a pin wheel mechanism, utilising the facility of the latter to provide at will either positive yarn feed control or a free running yarn.
An object of the invention is to overcome the disadvantages of mechanical drive arrangements and to provide more accurate yarn control. A further object is to provide yarn feed control devices and techniques which can utilise a pin wheel mechanism and thus retain the inherent advantages thereof, particularly the advantage of being able to change at will from a positive feed condition to a free running condition.